Re: [PATCH] KVM: SVM: Clear AVIC Physical ID table entry if vCPU creation fails

[Sean Christopherson <seanjc@google.com>]

On Wed, Sep 23, 2026, Naveen N Rao wrote:
> On Tue, Sep 22, 2026 at 12:36:15PM -0700, Sean Christopherson wrote:
> Yes, this LGTM, with a minor fix below.
> 
> > 
> > diff --git arch/x86/kvm/svm/avic.c arch/x86/kvm/svm/avic.c
> > index 3b037e385523..e767e43bfb40 100644
> > --- arch/x86/kvm/svm/avic.c
> > +++ arch/x86/kvm/svm/avic.c
> > @@ -395,6 +395,11 @@ static phys_addr_t avic_get_backing_page_address(struct vcpu_svm *svm)
> >         return __sme_set(__pa(svm->vcpu.arch.apic->regs));
> >  }
> >  
> > +static bool avic_is_addressable_vcpu(struct kvm_vcpu *vcpu)
> > +{
> > +       return vcpu->vcpu_id <= __avic_get_max_physical_id(vcpu->kvm, NULL);
> > +}
> > +
> >  void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb)
> >  {
> >         struct kvm_svm *kvm_svm = to_kvm_svm(svm->vcpu.kvm);
> > @@ -412,7 +417,6 @@ void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb)
> >  
> >  static int avic_init_backing_page(struct kvm_vcpu *vcpu)
> >  {
> > -       u32 max_id = x2avic_enabled ? x2avic_max_physical_id : AVIC_MAX_PHYSICAL_ID;
> >         struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
> >         struct vcpu_svm *svm = to_svm(vcpu);
> >         u32 id = vcpu->vcpu_id;
> > @@ -425,7 +429,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
> >          * avic_vcpu_load() expects to be called if and only if the vCPU has
> >          * fully initialized AVIC.
> >          */
> > -       if (id > max_id) {
> > +       if (avic_is_addressable_vcpu(vcpu)) {
> 
> Missing a negation there:
> 	if (!avic_is_addressable_vcpu(vcpu))

Heh, I discovered this literally ~10 seconds before reading your mail.  Hooray
for tests!

> ... which also means all three places are inverting the check, so you 
> could optionally flip the helper instead.

I'll keep it as is, Paolo generally prefers "positive" predicates, and I tend to
agree with him, e.g. it makes it the error paths more obvious (the above bug
notwithstanding).